The present invention relates to a method and an installation allowing, industrially, the setting in adsorbed state, on a porous support, of certain active compounds contained in natural or synthetic products. More precisely, such an operation will be effected after a preliminary phase during which said active compounds will be extracted from these products with the aid of a solvent taken to supercritical pressure, i.e. a fluid in supercritical state or a subcritical liquid.
In effect, it is known that bodies are generally known in three states, namely solid, liquid or gaseous, and that one passes from one to the other by varying the temperature and/or the pressure. Now, there is a point beyond which one can pass from the liquid state to the gaseous or vapour state without passing via a boiling or, inversely, a condensation, but continuously: this point is called the critical point.
It is also known that a fluid in supercritical state, i.e. a fluid which is in a state characterized either by a pressure and a temperature respectively greater than the critical pressure and temperature in the case of a pure body, or by a representative point (pressure, temperature) located beyond the envelope of the critical points shown in a diagram (pressure, temperature) in the case of a comparison with that observed in this same fluid in the state of compressed gas. The same applies to the so-called xe2x80x9csubcriticalxe2x80x9d liquids, i.e. liquids which are in a state characterized either by a pressure higher than the critical pressure and by a temperature lower than the critical temperature in the case of a pure body, or by a pressure higher than the critical pressures and a temperature lower than the critical temperatures of the components in the case of a mixture (cf. on this subject the article by Michel PERRUTxe2x80x94Les Techniques de l""Ingxc3xa9nieur xe2x80x9cExtraction by supercritical fluid, J 2 770-1 to Dec. 1999xe2x80x9d).
The considerable and modulatable variations of the solvent power of the supercritical fluids are, moreover, used in numerous methods of extraction (solid/fluid), fractionation (liquid/fluid), analytical or preparative chromatography, treatment of materials (ceramics, polymers . . . ). Chemical or biochemical reactions are also made in such solvents. It should be noted that the physico-chemical properties of carbon dioxide as well as its critical parameters (critical pressure: 7.4 MPa and critical temperature: 31xc2x0 C.) make of it the preferred solvent in numerous applications, all the more so as it does not present any toxicity and is available at very low price in very large quantities. Non-polar solvent, the carbon dioxide taken to supercritical pressure sometimes has a co-solvent added thereto, constituted in particular by a polar organic solvent whose function is to considerably modify the solvent power, especially with respect to molecules presenting a certain polarity, ethanol often being used to that purpose. However, certain compounds are more favourably extracted with a light hydrocarbon having from 2 to 5 carbon atoms, and more favourably, from 2 to 4 carbon atoms, at supercritical pressure.
One of the principal advantages of the methods using fluids at supercritical pressure as solvents resides in the facility of effecting the separation between the solvent and the extracts and solutes, as has been described in numerous publications and, for certain important aspects of implementation, in French Patent FR-A-2 584 618. The interesting properties of these fluids have, moreover, been used for a long time in solid-fluid extraction and liquid-fluid fractionation, as has been described in the article mentioned above.
In the event of the extracts or solutes comprising very volatile products, such as odorant products, the mere separation by partial decompression bringing about separation of the solutes and their collection by phase separation with the fluid, is not very efficient and the fluid, even partially decompressed, still contains substantial quantities of such substances. In order to separate these substances from the fluid before its recycling, it is known to use an adsorbent bed which will fix these substances and purify the fluid, as described for example in Japanese Patent JP-A-02139003.
Finally, it is known that the extraction of natural products by a fluid at supercritical pressure leads to extracts of very high quality which are increasingly used in numerous applications. However, such extracts, lie, moreover, the extracts obtained with other means such as for example extraction by organic solvent, are often in the form of very viscous or even pasty products which are not easy to handle, with the result that their incorporation in solid supports, the dosage and the mixture with a matrix and possibly other active principles, within a solid excipient, are very difficult. One is sometimes obliged to place them in solution in an organic solvent in order to effect impregnation of a solid excipient, which is regrettable since there thus disappears a determining advantage in numerous applications for which any contact of the product with an organic solvent is to be avoided.
The present invention has for its object to propose means making it possible, for purposes of industrial production, to extract active principles, particularly of pharmaceutical, cosmetological, dietetic interest, from diverse raw materials in which they are diluted, in variable concentration, depending on the origin of these raw materials and the period of their harvesting, as is always the case for products of natural origin, and to fix the extract obtained in the course of extraction in an adequate porous matrix by impregnation in one and the same operation.
According to the invention, the operation of extraction by fluid at supercritical pressure is coupled with a second operation during which the separation of the extract mixed with the solvent fluid and the impregnation of a porous medium by this extract are effected simultaneously.
The present invention thus has for its object a method for setting in adsorbed state, on a porous support, compounds contained in a product, in which, during a first step, the extraction of the compounds is effected by contacting the product with at least one solvent fluid at supercritical pressure leading to the obtaining of a mixture of extracts and of solvent fluid, characterized in that, in a second step, the water contained in the mixture of extracts and of solvent fluid is eliminated, the temperature and pressure conditions are adjusted so as to obtain, in an enclosure, two phases, namely a first phase essentially constituted by the solvent fluid in the gaseous state and a second phase constituted by a mixture of liquids formed by solvent fluid and extracts of the product, these two phases are made to trickle through a porous support adapted to adsorb the extracts, the solvent fluid contained in the second phase is vaporized.
The elimination of the water will preferably be ensured by causing the mixture of extracts and of solvent fluid to trickle over a bed of adsorbent product adapted to fix the water selectively.
The solvent fluid may be constituted by pure carbon dioxide, nitrogen protoxide or a light hydrocarbon counting from 2 to 4 carbon atoms. The solvent fluid may be pure or possibly have one of more co-solvents added thereto. For example, the solvent fluid may in particular be constituted by a mixture of carbon dioxide with at least one co-solvent constituted by an alcohol and preferably ethanol, by a ketone and preferably acetone, by an ester and preferably ethyl acetate.
The first step of extraction may preferably be effected at a pressure included between 7.4 MPa and 80 Mpa, and preferably between 10 MPa and 40 MPa, and at a temperature included between 0xc2x0 C. and 80xc2x0 C. Similarly, the trickling of the two phases through the porous support may be effected at a pressure included between 1 MPa and 10 MPa, and preferably between 4 MPa and 8 Mpa, and at a temperature included between 0xc2x0 C. and 80xc2x0 C.
The present invention also has for its object an installation for extraction/impregnation of the type comprising an extractor containing a product from which it is desired to extract the compounds, which is traversed to that end by at least one solvent fluid at supercritical pressure, characterized in that it successively comprises, downstream of the extractor, means for eliminating the water contained in the extracted compounds, means adapted to create, in an impregnation enclosure containing a porous medium, two phases, namely a first phase essentially constituted by the solvent fluid in the gaseous state and a second phase constituted by a mixture of liquids formed by solvent fluid and the extracts of the product, so as to effect the adsorption by the porous medium of the extracted compounds. The impregnation enclosure may comprise means for contributing enthalpy, particularly constituted by a double envelope with circulation of heat-exchange fluid.
The installation may also comprise, downstream of the impregnation enclosure, means for condensation of the solvent fluid.
In a variant embodiment of the invention, the extractor may be constituted by a fractionating column operating in counter-flow, adapted for the treatment of liquid raw materials.
Various forms of embodiment of the present invention will be described hereinafter by way of non-limiting examples, with reference to the accompanying single Figure which schematically shows an installation for carrying out the method according to the invention.
As has been described in detail in the article and the Patent mentioned hereinabove, it is known that the methods of extraction and of fractionation using a fluid at supercritical pressure comprise two successive steps: a first step during which the solvent fluid is contacted with the raw material to be treated, under such pressure and temperature conditions that its solvent power with respect to the compounds to be extracted is high, and a second step during which the fluid is placed under such pressure and temperature conditions that its solvent power is very weak with respect to the products which it has extracted from the raw material during the earlier step, which allows the separation of these extracts, the fluid then being recycled. Unlike the conventional embodiments consisting in separating the two phases obtained during this second step in gravity or inertia separators, the method according to the invention consists in causing the mixture of these two phases to trickle within a porous medium.
It has been noticed that, if the operation is carried out without particular precaution, the extracts are not distributed homogeneously on and within the porous medium and, even by proceeding with stirring of this porous medium if it is in pulverulent or granular form, for example with the aid of a rotating turbine, lumps of variable size are generally obtained, resulting from the agglomeration of the particles of the porous medium by the extracts which, instead of penetrating in the pores, remain on the surface without homogeneous distribution. Moreover, natural products, capable of being advantageously treated by a method of this type, always having a certain content of water, the extracts always contain water of which the presence complicates their adsorption on the porous supports or excipients, as the majority of them have a great affinity for water, so that their structure and their mechanical properties are seriously altered by the water thus contributed by the fluid at the same time as the extracts envisaged.
On the contrary, when the water is trapped, particularly by a selective adsorbent, and the impregnation of the porous medium is then effected under determined pressure and temperature conditions, it is observed that, surprizingly, the extracts impregnate this porous medium in very homogeneous and reproducible manner, leading for example to a non-sticky powder presenting a good fluidity in the case of the initial porous medium also presenting these characteristics.